Prostate secretory protein (PSP15) is one of the major secreted proteins in human prostate fluid. Several recent studies of human prostate fluid by high resolution two-dimensional gel electrophoresis have shown PSP15 to be a 15,000 MW acidic protein having an isoelectric point of 5.5-6.0 (D. B. Carter and M. I. Resnick, The Prostate, 3, pp. 27-33 (1982); Y. C. Tsai, et al., J. Clin. Chem., 30, pp. 2026-30 (1984). PSP15 is secreted by the epithelial cells of the prostatic acini.
PSP15 appears to be the evolutionarily conserved counterpart of prostate-binding protein (PBP) described previously in the rat, dog and cynomologous and rhesus monkeys and baboons, as determined by two-dimensional gel electrophoresis and by its relative abundance in the prostatic secretion (D. B. Carter, et al., "The Antigenic Relatedness of Proteins From Human and Simian Prostate Fluid", The Prostate, 6, 395-402 (1985)). PSP15 has also been referred to as Estramustinebinding protein and prostatin. In the rat, PBP is an androgen-regulated-protein of the prostate as evidenced by the absence of expression of PBP following castration.